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Couplage variable entre un qubit de charge et un qubit de phase

Abstract : We have studied the quantum dynamics of a superconducting circuit based on a dc-SQUID coupled to a highly asymmetric Cooper pair transistor (ACPT). The dc-SQUID is a phase qubit controlled by a bias current and magnetic field. The ACPT is a charge qubit controlled by a bias current, magnetic flux and gate voltage.

We have measured by microwave spectroscopy the lowest quantum levels of the coupled circuit as a function of the bias parameters. Quantum state measurements of the phase and charge qubit are achieved by an escape measurement on the dc SQUID with a nanosecond flux pulse applied to it. The measurement of the ACPT state consist of a new quantum process: the excited state of the ACPT is adiabatically transferred to the excited state of the SQUID during the flux pulse.

Our circuit enables the independent manipulation of each qubit as well as the entanglement of the quantum states of the two circuits. We observe avoided level crossings between the two qubits when they are put in resonance. The coupling strength is measured over a large frequency range and varies from 60 MHz to 1.1 GHz. In this coupled circuit, we succeed to realize a tunable coupling between the charge and the phase qubit. We have analyzed theoretically the quantum dynamics of our circuit. This analysis explains well the measured tunable coupling strength by a combination of a capacitive and a Josephson coupling between the two qubits.
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https://tel.archives-ouvertes.fr/tel-00310131
Contributor : Aurélien Fay <>
Submitted on : Thursday, August 7, 2008 - 5:32:20 PM
Last modification on : Thursday, November 19, 2020 - 1:00:33 PM
Long-term archiving on: : Thursday, June 3, 2010 - 6:05:22 PM

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  • HAL Id : tel-00310131, version 1

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Aurélien Fay. Couplage variable entre un qubit de charge et un qubit de phase. Matière Condensée [cond-mat]. Université Joseph-Fourier - Grenoble I, 2008. Français. ⟨tel-00310131⟩

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